A ball grid array IC socket (hereinafter, simply referred to as “IC socket”) is disclosed in U.S. Pat. No. 6,132,222 (FIG. 3). This IC socket comprises contacts for contacting pin contacts of an IC package. The contacts comprise contact arms for contacting the pin contacts, fixing portions for fixing the contacts to the insulative housing of the IC socket, and solder feet to be connected to the circuit board. Generally, the IC sockets are provided to consumers with solder balls soldered on to the solder feet.
In the known IC socket described above, the IC package has pin contacts. In the case that the IC package is a ball grid array (BGA) or a land grid array (LGA), the contacts of known IC sockets are modified to connect with the BGA or LGA contacts. The contact arms, which contact electrodes of the IC package, are curved after extending through an IC package mounting surface from the fixing portions, such that the contact points of the contact arms (i.e., the points on the contact arms that contact the contacts of the BGA or LGA) are horizontally offset. This horizontal offset reduces the height of the IC socket assembly having the IC package mounted thereon. The contacts of a ball grid array or a land grid array IC package are connected to the contact arms by application of a mechanical force. This construction is adopted in response to the miniaturization of products to which IC sockets are mounted.
For IC sockets with contact arms that are offset in the manner described above, it is preferable that the positions of the solder balls on the opposite side of the housing from the contacts, approach the positions of the contact points in the horizontal direction. That is, it is preferable that the solder feet are similarly offset from the fixing portions in the same direction as are the contact points of the contact arms. This offset is to balance the arrangement of the LGA or BGA of the IC package and the arrangement of the BGA of the IC socket.
Due to the recent and ongoing increases in the speed of transmitted signals, however, it is preferable that the signal paths of the contacts are as short as possible.
In view of the above, it is desirable that the solder feet are offset from the fixing portions, while providing the shortest possible signal paths from the IC package to the circuit board.
In the IC socket disclosed in U.S. Pat. No. 6,132,222, the solder feet are formed by bending the lower ends of the contacts, which extend downward from the fixing portions, at substantially a right angle. Therefore, in the case that the solder feet are to be offset, a problem arises in that the signal paths become elongated. In addition, solder fillets are formed between solder balls and the solder feet during soldering of the solder balls onto the solder feet. There is a possibility that the solder balls are pulled toward the right, that is, the side of the fixing portions, due to the surface tension of the molten solder fillets. This leads to the problem that the solder balls are formed on the solder ball pad at positions that deviate from their predetermined positions, where they are to be soldered to the circuit board. As a result, the positional accuracy of the solder balls will be deteriorated, thereby reducing the reliability of electrical connections. In addition, there is a risk that the spherical shapes of the solder balls will be altered due to the horizontal displacement thereof.